1. Field of the Invention
The present invention relates to a manufacturing method for organic EL devices used as display devices for computers and televisions or the like.
2. Background Art
EL (Electro-Luminescence) elements, which use organic materials as the luminescent materials are called organic EL elements, and the organic EL display devices using the organic EL elements have favorable features such as:
(1) high light emitting efficiency,
(2) low driving voltage,
(3) capability of displaying multiple colors,
(4) no need to use a back light because of its spontaneous emission of light,
(5) no dependency on angle of visibility,
(6) thin and light,
(7) high response speed,
(8) capability of using a flexible substrate.
Organic EL devices have therefore been drawing attention because they could take place of LCD (liquid crystal display) devices.
FIG. 9 shows a perspective view showing a schematic structure of an organic EL display device in the simple matrix system. On the surface of a transparent glass substrate 1 (substrate), a transparent anode 2 patterned in a plurality of stripes is formed, and on the anode 2, an organic positive hole transporting layer 3, an organic luminescent layer 4, an organic electron transporting layer 5 are formed.
The organic EL display device further comprises a cathode 6 patterned in a plurality of stripes so as to perpendicularly cross the above-described anode 2.
The anode 2 is formed, by first depositing an ITO (Indium Tin Oxide) film by a sputtering method or the like, and then by etching this ITO film for patterning a plurality of stripes formed in parallel to each other.
After depositing the organic film 7 onto the anode 2 by a vacuum deposition method such as a resistance heating method, the cathode 6 is formed by vacuum deposition methods such as a resistance heating deposition method, an electron beam deposition method, or by a sputtering method using a shadow masks for disposing a plurality of stripes in parallel to each other.
Alternatively, before formation of the anode 6, an electron injection layer made of an inorganic thin film such as an inorganic fluoride is first formed by vacuum deposition methods such as resistance heating, electron beam deposition, or by a sputtering method.
The above described anode 2 and cathode 6 are formed so as to perpendicularly cross each other.
The cathode 6 is usually formed using materials such as aluminum (Al), an alloy of magnesium and silver (Mgxe2x80x94Ag), an alloy of aluminum and lithium (Alxe2x80x94Li), or an alloy of magnesium and indium (Mgxe2x80x94In).
A deposition process of the thin film using the resistance heating method is usually applied to the formation of the cathode 6.
In this deposition process, deposition is executed by filling the above described deposition material into a deposition source, which is formed by processing high melting point metals such as tungsten, tantalum, or molybdenum, and by placing below the substrate 1 the deposition source filled with the deposition material. The deposition source is heated up to a predetermined temperature by flowing an electric current to the source and the material to be deposited is evaporated and deposited onto the substrate surface. In general, the deposition source has been placed directly below the center of the horizontally held substrate aiming to form the film in a uniform thickness or at a position, which is not directly below the center of the substrate but somewhere below the deposition region of the substrate because of the geometrical restriction of the deposition reactor.
When, for example, the shadow mask method is used for patterning the stripe shaped cathode 6, the shadow mask is formed using a thin metal plate by etching it for forming a plurality of stripes and the metal plate after being processed is closely attached to the substrate for further deposition process.
As described above, when the cathode 6 is deposited by placing the deposition source beneath the substrate as described above, in order to improve the opening ratio of the light emitting of cross sections between the cathode 6 and the anode 2, it becomes necessary to make the opening area of the metal mask wider by narrowing the metal stripe-like portions between the openings (slits).
Generally, the metal mask can be processed by various methods such as a laser processing method, an additive processing (electroforming) method, and a wet etching processing method. However, it is difficult for any of the above-mentioned methods to process a narrow space less than 0.1 mm.
Since the stripe-like portions between slits are mechanically weak, it is difficult to form a mask having such narrow metal stripes, due to deformation or breakage of the metal stripe-like portions.
A counter measure is disclosed in Japanese Unexamined Patent Application, First Publication No. Hei 10-50478, in which a reinforcing line is attached to the mask for preventing the deformation of the mask.
However, in conventional cathode forming methods, in order to obtain a desired pattern width of the cathode 6, it is necessary for the stripe-like metal portions between slits of the mask to have the same pattern width of the cathode 6, and as a result, the manufacturing process becomes complicated.
In contrast, when a mask for general use is used, it is not possible to make slit widths between cathode stripes of 0.1 mm or less, since it is not possible to form the original slit width of the mask to be less than 0.1 mm, and since it is not possible to make the slit width finer from the relative positional relationship between the substrate 1, the mask, and the deposition source. Thus, the problem of the conventional methods is that it is not possible to make the slit widths less than 0.1 mm.
When forming the organic films, which constitute lower layers of the cathode, the evaporated substances or the deposition materials perpendicularly impinge onto the organic film located around the center portion of the substrate beyond the deposition source. Thereby, the kinetic energy of the deposition materials or depositing atoms impinging on the organic films sometimes causes a local deformation or coagulation of the organic film and pin-holes are often generated in the organic films by the surface disorder or the change of the surface morphology of the organic films.
In addition, particles of the deposition materials (cluster) generated by the bumping of the deposition material in the deposition source impinge the organic film perpendicularly, which damages the organic film. Damage of the organic film by this phenomenon is particularly remarkable when the deposition material is oxidized or nitridized by the reactions with oxygen or nitrogen in air.
When the cathode 6 is formed on the thus-degraded organic films, the organic materials do not exhibit normal rectification characteristics due to a local field concentration by the disorder of the organic film or due to a short circuit by the pin-holes formed in the surface of the organic material.
An influence of the conventional cathode formation method on the operational characteristics of the conventional organic El display device is described with reference to FIG. 10 when being operated by a simple matrix driving method. FIG. 10 is a block diagram showing the structure of the organic EL display having a 6xc3x976 simple matrix structure.
When driving an organic EL display device having a simple matrix structure shown in FIG. 10 in a line sequential driving mode, the anode, assigned as the data electrode, is connected to a current source or a voltage source for applying a voltage which changes with data, and the cathode, assigned as the scanning electrode, is sequentially scanned at timings shown in FIG. 11.
At the time A shown in FIG. 11, when the scanning electrode S2 is turned into a LOW level (voltage is 0), an organic El element at an intersection between the data electrode I1 and an electric potential V1 is energized so that a current flows in the forward direction and the organic EL element emits light.
In contrast, when, for example, the intersection between the data electrode I3 and the scanning electrode S4 is short-circuited and the leak current flows in the reverse direction, the light emission region located at the intersection between the data electrode I3 and the scanning electrode S4 always becomes the non-lighting state.
As a result, at a time B in FIG. 11, since the potential between the scanning electrode S3 and the scanning electrode S4 is zero, the light emitting region (organic EL elements) in the display area except for a short-circuited region is energized in the forward direction and an electric current flows in the direction indicated by the arrow 9.
It becomes impossible to control the current to be supplied from the data driver to the lighting region at the time of selecting pixels when some organic EL elements are short-circuited.
Therefore, when the scanning electrode is turned on the LOW state according to the timing chart shown in FIG. 11, an extraordinary current will flow in the pixels except for the short-circuited pixel on the same data electrode I3 as that of the short-circuited organic EL element due to the potential difference of the scanning electrode S4.
As a result, during driving of the organic EL elements, pixels on the longitudinal line along the data electrode I3 are usually lit. As described above, the short-circuit of some organic EL elements cause non-lighting pixels or cross-talk.
The present invention is made to overcome those above-described problems and an object of the present invention is to provide a manufacturing method for an organic EL display device, capable of increasing the opening area of the display and making the pitch narrower so as to make the non-lighting space between pixels narrower.
An additional object of the present invention is also to provide a manufacturing method for an organic EL display device, capable of eliminating generation of short-circuited pixels in the organic El elements and to prevent generation of non-lighting defective pixels and cross-talk.
According to the first aspect of the present invention, an organic EL display device manufacturing method comprises: a first step of forming a first stripe-shaped electrode pattern on a substrate surface; a second step of forming a plurality of layers including an organic layer on the substrate surface including the first electrode pattern; and a third step of forming a second stripe-shaped electrode pattern on the first electrode pattern in the orthogonal direction to the first electrode pattern by disposing a mask between deposition sources of the electrode material and the substrate separated by a predetermined distance from the substrate and by supplying a deposition material onto the surface of the plurality of layers through slits of the mask; wherein, the deposition sources are provided at a position such that the deposition material is deposited onto the substrate surface at a predetermined incident angle.
According to the second aspect, in the above organic EL display device manufacturing method, a second deposition source is disposed at a position on a projected line at the position of the first deposition source in parallel with stripes of said second stripe-like electrode and which has the same distance as the first deposition source from the vertical line passing through the center of the substrate.
According to the third aspect, the organic EL display device manufacturing method further comprises: after the third step, a fourth step of rotating the substrate and the mask by 180 degrees about the vertical axis passing the center of the substrate, while maintaining a positional relationship between the substrate and mask; and a fifth step of forming the second electrode pattern in succession to the third step by supplying a deposition material for the electrode through slits of the mask.
According to the fourth aspect, in the organic EL display device manufacturing method according to claim 1, the incident angle of the deposition material onto the substrate is controlled by controlling a distance between the substrate and a plane which is parallel to the substrate, and which includes apertures of the deposition sources, and a distance between a projected point of the substrate center on the plane including apertures of the deposition sources and centers of the deposition sources.
According to the fifth aspect, in the organic EL display device manufacturing method according to claim 1, the substrate is disposed in the inclined state with a predetermined inclination angle from the horizontal plane, and the mask is disposed parallel to the substrate separated at a predetermined distance from said substrate.
According to the sixth aspect, in the organic EL display device manufacturing method according to claim 1, the incident angle of the deposition material onto the substrate surface is set within a range of 30 to 85 degrees.